Conventionally, a valve timing control apparatus, such as a vane-type control apparatus, hydraulically controls a valve timing of at least one of an intake valve and an exhaust valve. A camshaft is driven by a timing pulley or a chain sprocket synchronized with a crankshaft of an engine. Phase difference, i.e., an angular strain is generated between the camshaft and the timing pulley or the chain sprocket in the valve timing control apparatus to control the valve timing.
According to JP-A-9-217610, a stopper piston, which is received in a vane rotor, engages with an engaging hole formed in a housing member at a predetermined angular position, so that the vane rotor is restricted from rotating with respect to the housing member in a hydraulic vane-type control apparatus.
The stopper piston is forced by at least one of retarding hydraulic pressure and advancing hydraulic pressure, so that the stopper piston is pulled out of the engaging hole. Retarding hydraulic pressure is applied to the vane rotor on the retarding angular side. Advancing hydraulic pressure is applied to the vane rotor on the advancing angular side. Both the retarding hydraulic pressure and the advancing hydraulic pressure are applied to the stopper piston in the structure in JP-A-9-217610.
When the phase control direction is changed from the retarding angular side to the advancing angular side, both retarding and advancing hydraulic pressure are applied to the vane rotor. Subsequently, one of the retarding and advancing hydraulic pressure is reduced, so that the phase of the vane rotor is controlled to the retarding angular side or the advancing angular side. When the direction of the phase control is changed, both retarding and advancing hydraulic pressure are maintained such that the stopper piston is forced in the direction, in which the stopper piston is pulled out of the engaging hole. Therefore, the stopper piston is protected from moving to the engaging hole.
As shown in FIGS. 8A to 8C, a stopper piston 310 engages with an engaging hole 303, so that a vane rotor 304 is restricted from rotating with respect to a housing 300. In detail, when the angle of the vane rotor 304 reaches at a predetermined angle, which corresponds to a target phase PT, the stopper piston 310 engages with the engaging hole 303 formed in an engaging ring 302. Alternatively, the stopper piston 310 is forced by advancing hydraulic pressure, which is applied in a hydraulic chamber 320, and retarding hydraulic pressure, which is applied in a hydraulic chamber 322, so that the stopper piston 310 is pulled out of the engaging hole 303. As shown in FIG. 8A, when either retarding or advancing hydraulic pressure is applied to rotate the vane rotor 304 by a predetermined angle with respect to the housing 300, either advancing hydraulic pressure in the hydraulic chamber 320 or retarding hydraulic pressure in the hydraulic chamber 322 is applied to the stopper piston 310 in a direction, in which the stopper piston 310 is pulled out of the engaging ring 302. When temperature of hydraulic oil is high, viscosity of hydraulic oil decreases, and hydraulic pressure decreases. In this situation, when the angle of the vane rotor approaches the predetermined angle, the stopper piston 310 is urged by a spring 312, and protruded on the side of the engaging ring 302.
When a camshaft opens and closes an intake valve and an exhaust valve, the camshaft receives fluctuating torque. The fluctuating torque changes between the retarding angular side and the advancing angular side with respect to a crankshaft, and the vane rotor 304 is rotated to the retarding and advancing angular sides relative to the housing 300 due to the fluctuating torque. The stopper piston 310 collides against the inner wall of the engaging ring 302 (FIG. 8B). Subsequently, the stopper piston 310 engages with the engaging ring 302 (FIG. 8C) when the vane rotor is rotated toward the predetermined angular position due to fluctuating torque. As a result, the stopper piston 310 and the engaging ring 302 may be worn.
Alternatively, when the phase of the vane rotor 304 is controlled from the predetermined angular position to a target position with respect to the housing 300, retarding or advancing hydraulic pressure is applied to the vane rotor 304. Either hydraulic pressure in the hydraulic chamber 320 or hydraulic pressure in the hydraulic chamber 322 is applied to the stopper piston 310, so that the stopper piston 310 is pulled out of the engaging ring 302. In this situation, the vane rotor 304 may be rotated to the target angular position with respect to the housing 300 before the stopper piston 310 is completely pulled out of the engaging ring 302. As a result, the stopper piston 310 collides against the inner wall of the engaging ring 302 (FIG. 8B), and the stopper piston 310 and the engaging ring 302 may be worn.
In JP-A-9-217610, phase of the vane rotor 304 is controlled from a predetermined angular position to a target angular position when the engine is started. However, the phase control in JP-A-9-217610 is not performed by changing a phase control direction. Accordingly, the vane rotor 304 is controlled from the predetermined angular position to the target phase (target position) by either retarding hydraulic pressure or advancing hydraulic pressure. Therefore, the stopper piston 310 may collide against the inner wall of the engaging ring 302.
In another conventional valve timing control apparatus, the hydraulic chamber 322 is not formed, and the stopper piston 310 is pulled out of the engaging ring 302 by retarding hydraulic pressure in the hydraulic chamber 320. The stopper piston 310 engages with the engaging ring 302 at the most advancing position in the valve timing control apparatus. When the vane rotor 304 is rotated from the most advancing position to the retarding angular side, retarding pressure is generated in the hydraulic chamber 320 in a direction, in which the stopper piston 310 is pulled out of the engaging ring 302. In this structure, when only advancing pressure is applied to the vane rotor 304 to rotate the vane rotor 304 toward the most advancing angular position, retarding pressure is not applied from the hydraulic chamber 320 to the stopper piston 310. Accordingly, when the vane rotor 304 approaches to the most advancing angular position, the stopper piston 310 is urged by a spring 312, and is protruded into the engaging ring 302. As a result, the stopper piston 310 may collide against the inner wall of the engaging ring 302 by fluctuating torque applied to the vane rotor 304.
Furthermore, when the phase of the vane rotor 304 is controlled from the most advancing angular position, in which the stopper piston 310 engages with the engaging ring 302, to the retarding angular side, retarding pressure is applied to the vane rotor 304. The retarding pressure is also applied to the stopper piston 310, in a direction in which the stopper piston 310 is pulled out of the engaging ring 302. In this situation, when the vane rotor 304 is rotated to the retarding angular side before the stopper piston 310 is completely pulled out of the engaging ring 302, the stopper piston 310 collides against the inner wall of the engaging ring 302.